Resistor



v.' E. JOHNSON ET AL March 31, .1942.

REsIsToR Filed Oct. 29, 19:58

- 4 Sheets--Shee1I 1 Fig. 1.

Non l s ATTORN 1b INVENTORS WITNESSES:

)QM/M41 V. E. JOHNSON ET AL RESISTOR Marclfl 31, 1942.

4 Sheets-Sheet 2 Filed 001;. 29, 1938 llllllllu Fig. 4.

WITNEssEs: 'MVENTORS Ww Frank H lar/21er' Perry VStewart (l Q2) uwVidal-1.1011115011 H y A 61111133011 ATTO R N March 3l, 1942. v EJOHNSQN TAL 2,277,912

RES ISTOR 4 sheets-sheet :s

Filed Oct. 29, 1938 f INVENTORS Ffank H.Fa1m er Perry K Stemat' t,

WITNESSES:

Viet orEJohns lgA-J m1051011 BY Z ATTOR Y I March 31, 1942-4 v. E.JoHNsoN Erm. 2,277,912

RESISTOR y Filed Oct.. 29, 1938 4 Sheets-Sl'uaekI 4 l I l l 1 1 HnnnwwrFly. 8.

7 P6 @e P4 V 2 ,um 69 65 f 14v f Fry 9. y

WITNEssEs; 64 e '64 INVENToRs .e Franlfl Farmez; Perry I( Stewart,Vietorl Johnsonay AJ 1n P6011 ATTORNE Patented Mar. 31, 1942 UNITEDSTATES PATENT OFFICE RESISTOR Sylvania Application October 29, 1938,Serial No. 237,786

6 Claims.

Our invention relates generally to resistors, and it has reference, inparticular, to an improved construction for neutral grounding resistors.

In large polyphase power distribution systems, it is usually desirableto provide a grounding resistor between the neutral wire of the systemand the ground, for limiting the flow of fault current and assisting instabilizing the system when a ground fault occurs therein. The dutyimposed on neutral resistors is of a radically different nature thanthat imposed on ordinary control resistors, and While called upon tofunction at relatively rare intervals, they must at those timesl be ableto handle unfailingly and Without distress large currents for indefiniteperiods. Under normal conditions, the grounding resistor may carrycurrent for only a very short period of time, while under abnormalconditions, exceedingly heavy currents must be carried by the groundingresistor for relatively long periods of time of from one minute to tenminutes in extreme cases before the system is disconnected from thesource of power, or before the faulty section of the system is isolated.Since these grounding resistors are necessarily relatively large, owingto the peak currents and the extended periods of fault duration forwhich they must be designed, it is desir'- able to locate the resistorsout of doors adjacent to the point of ground connection of the system,so as not to use up valuable space within the station, or requireseparate housings therefor. It may, therefore, be seen that in generalit is d'esirable to provide a resistor which is not only capable ofwithstanding exceedingly heavy surges of current for extended periodswithout failure, but which is also unaffected by exposure to variedweather conditions.

Heretofore, it has been customary to utilize indoor mounted resistorscomprising a plurality of cast iron grid sections rigidly mounted onsupporting rods in 'a frame, for providing the necessary amount ofresistance and the desired current carrying capacity. Resistors of thistype were required to be thus protected as such construction necessarilyinvolves a large number of joints between adjacent grids, which, if thegrids are exposed to Weather, often become a source of trouble, sincecorrosion of the grid surfaces tends to increase the contact resistancebetween the 'adjacent grids. This results in excessive heating at thejoints, during the flow of fault current, so that the cast iron gridsmay become sufficiently overheated to melt. Failure of a neutralgrounding resistor under such conditions,

during the existence of a fault on the system, may result in serioussystem disturbances, disrupting the service at points quite remote fromthe source of the fault. Furthermore, resistor elements of this kind areinherently weak structurally and may become broken at any time,depriving the system of the ground protection the resistor is intendedto afford, thus requiring constant vigilance and testing to eliminatethe hazards of open circuits resulting from broken grids. A castresistor is inherently a low-temperature device, and when rated at ve orten minutes, becomes abnormally large and expensive.

Therefore, the object of our invention, generally stated, is to providean improved resistor of simple and rugged construction, which may beeconomically constructed and maintained, which is reliable in operation,and which will withstand continuous exposure to the weather and extremeheating and cooling cycles without deterioration or breakage.

A more specific object of our invention is to provide for utilizing, ina resistor, a non-corrosive continuous resistance element of a materialwhich will resist deformation at high temperatures, and for yieldinglysupporting the element in a frame to allow expansion and contraction ofthe element.

Another object of our invention is to provide for supporting orsuspending a fiexible strip resistance element in a rigid framestructure in such manner as to eliminate distortion thereof due toexpansion and contraction.

A further object of our invention is to provide for resilientlysuspending a continuous strip resistance element in a support frameWithout impairing the current carrying characteristics, or theventilation thereof.

Another object of our invention is to provide for supporting orsuspending a flexible strip resistance element formed in a zigzag shapein a supporting frame by utilizing insulating hangers connected to thereversely curved or bent portions of the element.

A further object of our invention isv to provide for forming aresistance element of the abovedescribed character in such manner thatit may be suspended in a frame by supporting it at the reversely curvedor bent portions only.

A still further object of our invention is to utilize a groundingresistor comprisingv a continuous stainless steel stripelement in theneutral ground connection of a power system.

A further object of our invention is to utilize a plurality ofyieldingly supported stainless steel resistor elements in a resistorunit to provide a compact and durable neutral grounding resistor.

Other objects will, in part, be obvious, and will, in part, appearhereinafter.

In a preferred embodiment of our invention, the resistor may comprise,generally, a continuous strip resistance element which is disposed to besupported in a rigid frame so as to allow for expansion and contractionof the element without subjecting the parts thereof to undue stress. Inorder to safely withstand the heavy current surges to which the resistormay be subjected when utilized, for example, for grounding the neutralpoint of a power system or the like, the resistance element comprisespreferably a strip of one of the nickel chromium alloy steels, commonlyknown as stainless steels, which is not only highly resistant tocorrosion, but which also retains a relatively high degree of mechanicalstrength even at relatively high temperatures, so that the resistor maybe safely operated at much higher temperatures than can cast iron gridresistors, thus permitting a marked reduction in the mass of theresistance element, and at the same time utilizing the greatly increasedohmic value of the resistance element at these higher temperatures forrestricting the flow of fault current.

For a further understanding of the nature and scope of our invention,reference may be had to the following detailed description, taken inconnection with the accompanying drawings, in which:

Figure l is a plan view of a portion of a resistor embodying a preferredform of our invention;

Fig. 2 is a side view of a spacer member used with the resistor of Fig.1;

Fig. 3 is an enlarged perspective view of a portion of the resistor' ofFig. l;

Fig. 4 is a side elevation view of a resistor construction comprising aplurality of the resistors of Fig. 1;

Fig. 5 is an enlarged perspective View of a portion of an alternate formof resistor construction;

Fig. 6 is a sectional view of the resistor of Fig. 5 along the lineVI--VI;

Fig. 7 is a sectional view of the resistor element of Fig. 6 along theline VII-VII;

Fig. 8 is a side elevation view of a different embodiment of ourinvention; and

Fig. 9 is an end elevation view in part of the I embodiment of Fig. 8.

Referring particularly to Figs. 1 and 2 of the drawings, the referencenumeral II) denotes generally a resistor comprising a frame I2 having astrip or ribbon resistance element I4 supported therein, so as to allowfor expansion and contraction of the element without subjecting parts ofthe resistor to undue stress.

The frame I2 may preferably be fabricated from structural steel shapes,in any suitable manner, so as to provide a substantially rigid supportfor the resistance element I4. As it is preferable to install neutralgrounding resistors outdoors on account of their size, without anyhousing or other protection from the weather, the frame I2 may beheavily galvanized or otherwise weatherproofed, so as to preventcorrosion.

In order to provide a resistance element for grounding the neutral pointof a system, having a high degree of resistance to corrosion, and a highdegree of mechanical strength at relatively high temperatures, so as toresist deformation and prevent sagging of the element at the relativelyhigh temperatures under which it may operate, we prefer to form theresistance element I4 from a strip of one of the nickel chromium alloysteels, commonly known as stainless steels. At temperatures ranging ashigh as 800 C. and 100 C., the short time tensile strength of stainlesssteel is of the order of 15,000 and 3,000 pounds per square inch,respectively, thus permitting the safe operation of the resistor attemperatures far above the safe operating temperature of cast irongrids, and materially reducing the mass of resistance element necessaryto dissipate a surge of energy in limiting a fault disturbance in thesystem.

In our preferred form of construction, a flat strip of stainless steelmay preferably be formed flatwise into a plurality of substantiallyparallel back and forth turns, having rounded U-shaped ends I6therebetween, which is commonly referred to as a zigzag shape. Ifdesired, the straight portions of the back and forth or zigzag turns maybe stiff'ened, by providing them with one or more longitudinalindentations It through a suitable pressing operation, thus giving theresistance element a dished cross-section, as shown in Figs. 6 and '7,for the purpose of preventing undue vibration of the element andincreasing its resistance to deformation. Insulating spacers I9, whichare clearly illustrated in Figs. l and 2, may be provided, comprising aplurality of spaced apart fingers 2D which may be disposed between theadjacent straight portions of the resistance element, near the centralportion thereof, to further increase the rigidity thereof. Connectionmay be made to the resistance element I4 in any suitable manner, such asby connecting a bus bar 22 directly to the resistance element bysuitable means, such as the bolts 23, which may be reinforced by weldingif desired.

Support members 20 may be provided `for supporting the resistanceelement Iii in the frame I2 so as to provide for a yielding orlost-motion connection therebetween. In a preferred form, as is clearlyshown in Fig. 3 of the drawings, the support member 28 may comprise asubstantially flat strip of stainless steel, or other suitable material,having a reasonable degree ol flexibility and of sufficient width toprevent undue side sway, one end of which is preferably bent ilatwise ata slight angle to vthe main body, and subjected to a forming operationto provide upstanding edges 29 by which it may be connected to theresistance element III at the rounded U-shaped end portion Iii, being,for example, welded thereto. The other end of the support member 28 maybe connected by any suitable means, such as the bolts 29, to aninsulator support 30 which comprises, i'or example, a substantiallyhollow body member oi a refractory material, having a flanged baseportion 32. In this manner, We provide a flexible hinge or support forallowing expansion and contraction ol' the resistance element I4 withoutsubjecting it to undue stress.

Bracket members may be provided for securing the insulator supports tothe frame I2, comprising, for example, channel members having inturnedlongitudinal edges 30 and S'I which are disposed to form a longitudinalpocket in Which the flanged base portions 32 of the insulator supports30 may positioned. By utilizing such a form of construction, theinsulator supports 3B may be readily slid into position through the openend ol the bra ret members 35. If desired, the edge portion 3l of thebracket member may comprise a separate member removably secured to thebase thereof, and upon removal thereof, any or all of the insulatorsupports 30 may be removed, and cleaning or repairing thereof may beeasily effected when desired. In order to provide further insulationbetween the resistance element I4 and the frame I2 of the resistor, thebracket members 35 may be positioned in the frame I2 by being mounted inany suitable manner on insulators 4u, which are secured to the frame.

Referring particularly to Fig. 4, it may be seen that a compact andefficient resistor may be provided by combining a number of resistors,such as illustrated in Fig. l, in stacked relation, utilizing eitherseparate frame structures or a single frame having a plurality of pairsoi support brackets 35 secured thereto in the manner hereinbeforedisclosed in connection with Figs. 1 and 2. Suitable connection may bemade between the ditferent tiers o f resistance elements I4 by theconductor 22, which may be easily connected to the resistance elementsby any suitable means, such as the bolts 23, and welded, to provide anintegral connection with no loose connections to corrode or become open.

Referring to Figs. 5, 6 and '7, which illustrate details of an alternateform of resistor construction, the reference number 135 designates amodied form of support member which is disposed to be secured to therounded end portion I6 of the resistance element i4 for supporting theresistance element in the frame I2 and providing a yielding orlost-motion connection therebetween, so as to permit expansion andcontraction of the element without subjecting it to undue stress.

The support member 45 may, as indicated particularly in Figs. and (i ofthe drawings, comprise a C-shaped body, preferably formed by bending alength of stainless steel strap flatwise, and providing a suitable wearbushing 41, located in the central portion of the body for reducingfriction and eliminating localized wear. Parallel slots may be cut inthe lip portions of the support member 45, and the centrally disposedtongue portion 4B dened thereby may be bent outwardly to occupy theposition shown in dotted lines in Fig. 6. By then placing the lipportions of the support member 45 against the resistance element I4 andbending the tongue portions 43 inwardly about the resistance element,the support member 45 may be secured to the resistance element withoutimpairing the current carrying capacity of the element, and withoutproviding too ready a path for the flow of heat from the resistanceelement to the means of support, thus facilitating high temperatureoperation of the resistance element.

In order to yieldingly support the resistance element in the frame I2and provide for relative motion therebetween, support insulators 49 maybe provided, having an extending support pin 5I] which is disposed toeffect a sliding t in the bushing 4T of the support member 45. In thismanner, the resistance element I4 may be properly supported in the frameI2, and yet free to expand and contract without setting up unduestresses. I'f desired, suitable baffle members or cooling ns 52 may beprovided in connection with the support pins 5D, for additionallyreducing the flow of heat between the resistance member and theinsulators 49, and permitting the resistance element I4 to operate at ahigher temperature, thus further reducing the required amount of mass ofthe element.

In Figs. 8 and 9 a different embodiment of our invention is illustratedwherein a flexible stainless steel resistance element I4 is disposed tobe suspended in looped relation in a rigid frame structure 60, which maybe of any suitable form, comprising, for example, structural steelmembers or pipe members.

In a preferred form of construction, horizontal side members 62 may besecured to the frame 60 and provided with suitable insulator members 64secured thereto in any desirable manner, such as by means of the clamptype brackets 65 for positioning upper and lower support members 66 and68. These support members may, for example, comprise suitable lengthsor" pipe having a plurality of oppositely disposed laterally extendingfingers B9. Grooved insulating spools 'i2 of a rerractory material maybe positioned on the ngers G9 for supporting the resistance element I4.If desired, these spools may be secured to the fingers 39 so as to berotatable thereon, for a reason which will be hereinafter explained indetail.

Suitable saddle members "I4 and It may be provided for securing theupper and lower support members @Si and 63, respectively, to theirrespective insulator members Gi. The support members may be providedwith suitable means, such as the projecting pins i8 for engagement withopenings in the top or" the saddle members so as to prevent rotation oi'the support members therein. By making the throat portion of the lowersaddle member 'It sufciently deep, provision may be made for relativevertical movement of the support member t2 therein.

The resistance element I4 may then be suspended from the upper supportmember 66 by looping the element I4 alternately about successive spoolsl2 of the upper and lower support members to provide a plurality ofzig-zag back and forth turns. Ey looping the element I4 about theinsulator spools 2 of the upper and lower support members with the lowersupport member G8 in a raised position in the saddle member 1G, amoderate loading may be placed upon the loops of the resistance elementI4 because of the downward force exerted by the lower spacing member 55,so that the back and forth portions thereof may be maintained intension, unaffected by expansion of the element when under load, or thesubsequent contraction thereof when cooling after the load is removed.Since the spools 72 arev rotatable upon the fingers 69, uneven expansionor" the resistance element may be compensated for, as the element maymove relative to the points of support. The turns of the resistanceelement may thus be maintained under a constant tension and the spacingbetween successive turns may be maintained without the necessity ofintermediate spacers or support members.

It may be seen from the above detailed description, taken in connectionwith the accompanying drawings, that we have by our invention providedan improved construction for resistors whereby a non-corrosivecontinuous strip resistance element may be supported in a rigid frame insuch a manner as to allow for expansion and contraction of the elementwithout impairing the current carrying capacity thereof. With theresistance element secured to the support members in the mannerhereinbefore disclosed, the transfer of heat from the element to thesupporting insulators is reduced to a minimum, so that the element maysafely operate at relatively high temperatures. By utilizing commercialstainless steel, which may be easily secured in any desirable length,thickness and Width, a resistance element may be provided which has ahigh cooling factor, a high degree of resistance to corrosion, and ishighly resistant to deformation, even at relatively high temperatures.Accordingly, We are able to provide a neutrai grounding resistor ofrugged construction, having a non-corrosive high strength resistanceelement wherein the number of joints is held to a minimum, which willnot fail when subjected to a heavysurge of current, and Which maycomprise a reduced mass because of the permissible higher operatingtemperatures, thus insuring the reliability of the resistor in service,and a low cost of maintenance.

While our invention has been found of particular value in connectionwith applications of neutral grounding resistors, Where sudden andexcessive surges of fault current must be carried, it is to beunderstood that the invention is not intended to be limited to suchapplications, and may be readily and advantageously used Wherever aneconomical, reliable resistor is desired.

Since certain changes may be made in the above construction, anddifferent embodiments of the invention may be made Without departingfrom the spirit thereof, it is intended that all matter contained in theabove description or shown in the accompanying drawings, shall beconsidered as illustrative, and not in a limiting sense.

We claim as our invention:

1. A resistor comprising, a frame structure, a resistor element formedof a relatively wide strip of flexible material bent ilatvvise toprovide a plurality of substantially horizontal back and forth turns onedge and having a Width sufficient to prevent undue sagging of thecenter portions oi the turns when supported only at the ends, aplurality of insulating members supported by the frame structure inspaced relation with the said ends of the back and forth turns, andconnecting means interposed between the insulating members and the endsof the back and forth turns for supporting said resistor element fromsaid insulating members, said connecting means comprising relativelywide vertically rigid metal support members rigidly secured to said endsof the back and forth turns and having a limited area of contacttherewith to reduce the heat flow to the insulating members, and meansconnecting the support members to the insulating inembers to provide asubstantially rigid vertical support for supporting the ends of the saidturns in spaced relation to the insulating members, said connectingmeans functioning to provide a support yieldable horizontally in thelongitudinal direction of the back and forth turns to permitlongitudinal expansion and contraction of the back and forth turns andsupport the bach and forth turns rigidly in the vertical direction.

2. A neutral grounding resistor comprising, a frame, insulating supportmembers removably supported thereby, a continuous strip resistanceelement comprising a plurality of substantially horizontal back andforth turns on edge, means comprising metallic support members havingthe ends rigidly secured to the resistance element adjacent the oppositeedges thereof at the ends of the said turns and having openingsintermediate the ends, and support means projecting from the insulatingsupport members positioned in said openings for connecting theresistance element to the insulating support members and rigidlysupporting the resistance element vertlcally in the frame in spacedrelation to the insulating support members without appreciably stressingthe turns longitudinally to allow longitudinal movement of the ends ofthe turns of the element relative to the frame.

3. A resistor comprising, a frame, a horizontally disposed resistanceelement having a plurality of back and forth turns of stainless steelribbon on edge with a width sufficient to render the turnsself-supporting when supported at the end thereof, a plurality ofoppositely disposed insulator supports removably secured to the frame,and means comprising a plurality of flexible hanger members forresiliently supporting the resistance element at the said ends from theinsulator supports Without appreciably stressing the turnslongitudinally for movement in a horizontal direction only to providefor expansion and contraction of the resistance element.

Ll. A resistor comprising, a frame, insulating means disposed to beremovably secured to the frame, a plurality of substantially horizontalback and forth turns of flexible resistance ribbon formed from anon-corrosive nickel chromium alloy steel having a high temperature ofdeformation, and resilient support means comprising a plurality ofhangers dependent from the insulating means disposed to support theresistance ribbon in yielding relation with the insulating means Withoutappreciably stressing the resistance ribbon longitudinally.

5. A resistor comprising, a frame, a plurality of insulating memberssupported by the frame, a resistance element comprising a plurality ofsubstantially horizontal back and forth turns formed from a continuousstrip of resistance material, and a plurality of substantially fiathanger members dependent from the insulating members connected to theresistance element at fixed points so as to permit movement of saidpoints only in the longitudinal direction of expansion and contractionof the spaced turns of the resistance element.

6. A resistor comprising, a frame, a continucus ribbon resistanceelement comprising a plurality of substantially horizontal back` andforth turns, a plurality of insulating members supported by the framehaving metallic pins projecting substantially horizontally therefrom,and means comprising substantially C-shaped support members rigidlyconnected to the resistance element at the ends of the back and forthturns having openings, for receiving the metallic pins, said pins andsupport members functioning to slidably support the resistance elementon the pins in spaced relation to the insulating mem bers.

VICTOR E. JOHNSON. FRAITK H. FARMER. RAY A.. SIMPSON. PERRY V, STEWART.

